E1558. The Impact on Reproducibility of Shear Wave Elastography Measurements by Varying the Size of an Elastogram Region of Interest
  1. Andrew Zaleski; University of Calgary
  2. Oluwatoyosi Owoeye; Doisy College of Health Sciences, Saint Louis University
  3. Preston Wiley; McCaig Institute for Bone and Joint Health, University of Calgary
  4. Tate HubkaRao; University of Calgary
  5. Luz Palacios-Derflingher; Sports Injury Prevention Research Centre, University of Calgary; University of Calgary
  6. Richard Walker; McCaig Institute for Bone and Joint Health, University of Calgary; University of Calgary
  7. Carolyn Emery; Sports Injury Prevention Research Centre, University of Calgary; University of Calgary
The study objective is to assess the reproducibility of velocity and stiffness measurements of the proximal patellar tendon obtained by varying the region of interest (ROI) size on shear wave elastograms.

Materials and Methods:
Local institutional ethics committee approval was obtained. The study was designed as a nested case-control study within a larger prospective cohort study. High school basketball players between the ages of 13-18 years were recruited. Shear wave elastography (SWE) of bilateral proximal patellar tendons in longitudinal axis was performed using a standardized protocol and scanning parameters by a medical sonographer and supervised by a fellowship-trained musculoskeletal radiologist, both blinded to case-control status of study participants (presence of absence of patellar tendinopathy (PTP)). Elastograms were analyzed by a single observer by creating 4 circular ROIs, with 2 measurements equal to full anteroposterior (AP) tendon dimension (maximal ROI) and 2 measurements equal to 50% AP tendon dimension (half ROI) centered within the tendon. All measurements were obtained 1cm distal to the inferior patellar pole. Velocity(m/s) and stiffness(kPa) results were recorded for each ROI. Bland-Altman plots were created to evaluate differences between measurements for each ROI (maximum and half).

52 subjects (mean age 16.1 +/- 1.2 years, range 13-18 years; 23.4% female) were recruited (104 patellar tendons). Data from 5 participants were considered suboptimal for analysis and excluded, leaving 47 participants (94 tendons) for analysis. The difference between the first and second value obtained for velocity and stiffness for each tendon using a maximal ROI and a half ROI was calculated and displayed on Bland-Altman plots for comparison. For tendon stiffness, the half ROI difference range was –25 to + 35kPa while the maximal ROI difference range was –9 to +13kPa. For velocity, the difference range for half ROI’s was –0.74 to +1.2m/s while the maximal ROI difference range was –0.34 to +0.44m/s.

Tendon stiffness and velocity measurements on shear wave elastograms show less variability of the differences when employing maximal tendon thickness ROI. Heterogeneity of shear wave elastograms may contribute to less reproducibility of measurements obtained using half thickness ROIs. Maximal thickness ROIs may afford more reproducibility due to ease of placement. The clinical significance of this observation requires further study. When analyzing shear wave elastograms, we recommend employing an ROI equal to the full AP thickness of the tendon in longitudinal axis.